Although I'm not 100% sure if this difference in sound quality is the mapper's fault, but that's what I assume since the other sound channels sound fine.

It won't be possible to recreate it 100%. The author has done a fantastic job as it is. As he says in this thread: "Sunsoft 5B has a real analogue DAC, while the FPGA is feeding a digital I/O pin with a massively oversampled (50MHz sampling rate) and dithered waveform of the audio waveform signal."

I've used the same version infinest posted in that video. It's running on an older version of the OS though. I remember that I didn't update because the sound balance got worse with a new OS version on my unmodded AV Famicom.

Although I'm not 100% sure if this difference in sound quality is the mapper's fault, but that's what I assume since the other sound channels sound fine.

It won't be possible to recreate it 100%. The author has done a fantastic job as it is. As he says in this thread: "Sunsoft 5B has a real analogue DAC, while the FPGA is feeding a digital I/O pin with a massively oversampled (50MHz sampling rate) and dithered waveform of the audio waveform signal."

That wasn't my point. He did do a fantastic job (as shown in blizzz's comparison). I was just wondering why blizzz's everdrive n8 sounded better than mine.

I've used the same version infinest posted in that video. It's running on an older version of the OS though. I remember that I didn't update because the sound balance got worse with a new OS version on my unmodded AV Famicom.

I've tried all the way through version 10-16 of the OS. Did you use a version earlier than that which isn't listed in krikzz's OS downloads?

Wanted to post my findings in hopes of helping others with this issue.

I found that the low audio volume has to do with the ROM itself (why this is, I can't explain). Using the original Japanese rom, regardless of the mapper I tried, always had the low audio. This was also independent of the OS version as well.

What I did find is that the patched US rom worked flawlessly after trying the mapper posted in this thread. In other words, if your audio is low, try a different ROM. I doubt I can link directly to the working ROM, but it shouldn't be hard to find.

Ok I'm dumb. I thought the PAL Mr Gimmick has the 5B audio, but apparently it's only the Japanese one. And Batman wasn't frozen, it just doesn't work right with my arcade stick(PS360+). And it isn't supposed to have extra audio at all.

No official US or EU game has extra audio since they weren't wired for it. While it sounded slightly low on the AVS (which is adjustable), the 5B audio in the JP Gimmick! definitely plays for me, as well.